Is the word hardly a noun?

No, the Word 'hardly' is an adverb, a Word used to modify a verb, an adjective, or another adverb.

A noun is a Word for a person, a place, or a thing.

Example functions:

He hardly touched his dinner.

• The adverb 'hardly' modifies the verb 'touched'.
• The noun in the sentence is 'dinner', a Word for a thing.

Maggie is hardly new at this.

• The adverb 'hardly' modifies the adjective 'new'.
• The noun in the sentence is 'Maggie", a Word for a person.

This city is hardly ever quiet.

• The adverb 'hardly' modifies the adverb 'ever'.
• The noun in the sentence is 'city', a Word for a place.